This invention relates to a heat exchanger made of aluminum, (the word aluminum in this specification means aluminum as well as aluminum alloy) and a method for making the aluminum heat exchanger. The heat exchanger as this invention has a preferred usage of an evaporator for a refrigerant circuit, such as the evaporator of an automotive air conditioner.
Conventionally, such an evaporator has the problem that moisture is condensed on the surface thereof and drops off. Such droplets hinders the air flow passing through the evaporator. The droplets held in the evaporator reduces its heat exchanging efficiency, and also the droplets cause the problem that they are scattered downstream with the air flow.
Also the droplets held between fins of the evaporator causes rust on the fins.
Recently, such aluminum heat exchangers have been treated with a surface treatment in order to obtain an effective resistance to corrosion and impart a hydrophilic property. One embodiment of this surface treatment is explained hereinafter. Chemical conversion treatment, such as chromating, phosphating, which improves resistance to corrosion, is so applied that the aluminum base material 7 (shown in FIG. 5) which is used as the fin is covered with the chemical conversion coating 12. After the chemical conversion coating 12 is applied, inorganic material, such as silica particulates or silicate, which provides an effective hydrophilic property is so coated over the coating 12 that a coating 13 of inorganic material is made.
However, the inorganic material is easy to be removed after the fin has been used for a while, so that the organic material has a tendency to be scattered as particulates. The hydrophilic efficiency and the resistance to corrosion is, therefore, reduced. Furthermore, the particulates of the inorganic material stimulates operators' noses and makes them feel uncomfortable.
The aluminum heat exchanger has its fins covered by an Al--Si type brazing material containing a lot of silicon in order to braze the tube and the fins. Therefore, an eutectic crystal 11 (shown in FIG. 5) made from aluminum and silicon remains on the surface of the aluminum base material of the fin after brazing. Since the chemical conversion coating 12 is difficult to be deposited on the eutectic crystal 11, the problems described above become more serious.
The present invention has the object of solving such problems. The object of this invention is to reduce the scattering of the particulates even after the heat exchanger is used for a long while. A further object of this invention is to provide an aluminum heat exchanger which has an effective hydrophilic property (wettability) and a resistance to corrosion. A still further object of this invention is to provide a preferred method for producing the aluminum heat exchanger.